Zeolites and alumina have been used in the past in the preparation of catalysts for the production of aromatic hydrocarbons from aliphatic hydrocarbons. The alphatic hydrocarbon is passed over the catalyst at an elevated temperature in the liquid or vapor phase. Zeolites of various types have been suggested for the preparation of such catalysts. Examples of such zeolities are mordenite and the ZSM varieties, some of which contain gallium as ions which have been impregnated on the zeolite substrate or for which the original cations have been exchanged. However, it has sometimes been considered desirable to improve the yields of aromatic hydrocarbons when using such catalysts.
U.S. Pat. No. 4,180,689 teaches that by using catalysts which contain gallium and which are prepared from specific types of aluminosilicates, improved yields of aromatic hydrocarbons may be obtained if the gallium-containing catalysts are prepared from specific types of aluminosilicates. This patent further discloses that if the gallium is either exchanged for one of the cations or protons or impregnated into the zeolitic cavities, surprisingly high catalytic activity and selectivity are obtained, especially in hydrocarbon conversion process. The feed for this process is a C.sub.2 -C.sub.12 feedstock of either a single component or mixtures of saturated and unsaturated hydrocarbons.
U.S. Pat. No. 4,120,910 discloses that aromatic compounds can be produced by contacting, in the absence of added air or oxygen under suitable conversion conditions, a gaseous, paraffinic feed stock containing a high percentage of ethane with a ZSM-5 type crystalline aluminosilicate zeolite catalyst having incorporated therein a minor amount of a metal or metal oxide from Group VIII, IIB, or IB of the Periodic Table. Especially preferred is a zinc-copper mixture.
U.S. Pat. No. 4,304,686 teaches the aromatization of aliphatic hydrocarbons utilizing as catalyst a zeolite having an alumina-silica ratio of 10:1 to 500:1 in which at least some of the cations have been exchanged for gallium ions.
U.S. Pat. No. 4,350,835 teaches a catalytic process for converting a feedstock comprising a high percentage of ethane to aromatics employing as a catalyst a zeolite with a silica-alumina ratio of at least 12 and having incorporated therein a minor amount of gallium.
European Patent Specification Publication No. 50,021 teaches a process for producing aromatic hydrocarbons by contacting a feedstock containing at least 70% by weight of C.sub.2 hydrocarbons with a catalyst comprising an aluminosilicate with a silica-alumina molar ratio of at least 5:1 and in which either gallium is deposited thereon, or cations have been exchange with gallium ions.